(If you want to step up your Acoustics Database, and take your good enough studio to actually multiple levels ahead, this is the first chapter of your holy text (No exaggeration)!)
Welcome, class! (pun intended :P) While the world is full of velocity absorbers being disguised as BASS TRAPS making a fool out of the layman to earn a good fortune, not many people really know what it takes to really absorb or rather "TRAP" those low SUB bass frequencies. Today, we embark on a journey to unravel the mysteries of diaphragmatic membrane sound absorbers. These remarkable devices leverage the principles of physics to trap those untamable room modes in the SUB 100, or better yet, SUB 50Hz range! In this blog, we'll delve into the inner workings of these absorbers, demystify the math and physics behind their effectiveness, and equip ourselves with the knowledge to enhance acoustics. So, let's dive in and explore the fascinating world of diaphragmatic membrane sound absorbers together!
(This blog focuses on the functioning of a Membrane System, and the next scheduled blog is targeted to educate the readers on how the "easily accessible porous material" such as Rockwool can be specifically used to obtain the highly efficient low-frequency absorption of a membrane system. Make sure you subscribe to our newsletter to get notified as we post the blog! More blogs on Limp Mass, Helmholtz, and other complex systems are in queue!)
Before we jump into the specifics, let's grasp the fundamental concept of sound absorption. When sound encounters a material, it can be reflected, transmitted, or absorbed. Today, we focus on the absorbing aspect, where sound energy is converted into heat or mechanical energy. This absorption phenomenon reduces unwanted reflections and reverberations, leading to improved acoustics.
Now, with absorbers, there are two kinds: Velocity-based absorbers/traps and, second, Pressure based Absorbers/traps. We have already discussed a fundamental about velocity absorbers in a previous blog, as linked. But they have a lower limit of absorption when we are talking about Room Modes. (If it is a new term for you, in short, a room has a certain Frequency, above which it reflects sound, and below that frequency, it resonates on certain frequencies when generated by a speaker inside the room. These resonating frequencies are basically natural frequencies of the room surfaces, and are also known as Room Modes).
Now, for taming these unforgiving room modes, velocity absorbers fall flat. These little loose fibers can't do enough to dampen the rigid walls from vibrating, especially in solid core or concrete walls, and neither can they do anything to stop those nasty larger-than-life wavelengths of low-frequency sound to excite the room modes.
Here, pressure-based absorption comes into play, which in a nutshell produces counter resonance at those specific frequencies when triggered, and traps them inside, hence stopping the sound to interfere with the room in a way. A reason, why they are also known as resonance absorbers.
Resonance/ Pressure absorbers are preferred in two models: 1) Helmholtz Resonators, 2) Diaphragm or Membrane Absorbers. We will be discussing the latter today!
As discussed, the key principle behind diaphragmatic membrane sound absorbers is resonant absorption. This powerful mechanism enables these absorbers to selectively absorb sound within specific frequency ranges. How does it work, you ask? Well, it all revolves around the interaction between sound waves and vibrating membranes. These absorbers capitalize on this interaction to achieve targeted absorption.
To truly comprehend the "magic" behind diaphragmatic membrane sound absorbers, we need to understand the concept of a mass-spring system. Imagine the diaphragm as a "mass" encompassing the weight of the diaphragm itself and the air within the cavity behind it. Now, think of the diaphragm's flexibility as the "spring." Together, they form a resonator that vibrates at a specific frequency known as the resonant frequency. This frequency determines the absorber's effectiveness within a given range.
Impedance Matching: Unlocking Efficiency-
An essential aspect of diaphragmatic membrane sound absorbers is impedance matching. Picture this: the diaphragm is meticulously designed to possess an impedance that aligns with the air within the cavity. This careful matching facilitates efficient energy transfer from sound waves to the diaphragm, resulting in enhanced absorption capabilities. Impressive, isn't it?
Viscous and Frictional Damping: Transforming Sound Energy-
Now, let's explore the mechanisms that convert sound energy into other forms within diaphragmatic membrane sound absorbers. As the diaphragm vibrates in response to incoming sound waves, it encounters two critical damping mechanisms: viscous and frictional damping. Viscous damping arises due to air viscosity, while frictional damping stems from internal friction within the diaphragm material, and both of these are further facilitated by the addition of another damping agent which usually is a semi-rigid porous open-cell fiber. These damping mechanisms work together to convert sound energy into heat, effectively reducing the amplitudes of sound waves.
Tuning and Performance: Unleashing Potential-
The resonant frequency of diaphragmatic membrane sound absorbers can be fine-tuned by adjusting parameters such as diaphragm tension, mass, and size. This allows for targeted absorption within specific frequency ranges. By strategically placing multiple absorbers, we can manage a wide spectrum of frequencies, ensuring optimal acoustics tailored to our needs. Isn't that remarkable? But so is the difficulty of critical calculations to make them work as intended!
Placement and Configuration: Harnessing Power-
Careful placement and configuration play a vital role in unleashing their full potential. These absorbers are typically mounted on walls or within enclosures, strategically positioned in areas where sound pressure is the highest. This is usually the room boundaries, and accumulation of pressure from two dimensions occurs at the corners (this concept gave birth to the misconceptions of using velocity absorbers in the corners and thinking them as of BASS TRAPS. An entire blog is dedicated to this topic and is already queued in for the coming month. Subscribe to stay tuned!). Thoughtful placement ensures effective absorption and control over the acoustics of a room or space. So, attention to detail is key!
Here are a few companies that are actually making some good Pressure Absorbers and worth every penny:
1) RPG Modex
3)RealTraps - MegaTraps (Hybrid Velocity+Pressure Traps)
4) GIK Monster Bass Trap with FlexRange Technology (Hybrid Velocity+Pressure Traps)
At GrayVee Acoustics, we are not currently manufacturing any membrane units for sale, however, a leak :P reveals that we are working on something that sounds like Variable tuning Bass Traps. Isn't that interesting? Stay tuned for the full leak (again, subscribe to the newsletter ;)
Diaphragmatic membrane sound absorbers offer an exciting avenue for enhancing acoustics by harnessing the principles of physics. Through sympathetic resonance, impedance matching, damping mechanisms, and careful tuning, these absorbers provide targeted absorption within specific frequency ranges. Armed with this knowledge, you can create optimal acoustic environments for various settings, whether it's a home theater, recording studio, or peaceful workspace. So, keep exploring the wonders of acoustics and embrace the power of diaphragmatic membrane sound absorbers!
P.S. - I am literally laughing my *ss out while realizing how weirdly dramatic language I have used for educating about such a critical physical phenomenon XD! I swear, I didn't smoke anything before writing this, lol!
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